1. Field of the Invention
The present invention relates to a plant growth regulator and an object of the present invention is that said regulator is (1) able to suppress a spindly growth especially at the stage of raising the crop plants, (2) able to improve the long-term storage of seedling and (3) able to conduct an efficient regulation of raising of seedling whereby improvement in productivity of agricultural products is aimed.
2. Description of the Related Art
In recent years, agricultural techniques have been directed, both domestic and abroad, to the agriculture of an environment-protecting type and there has been a demand for agricultural technique which is friendly to ecology. Under such circumstances however, it is still the present status that agricultural chemicals are used for prevention of plant diseases and that they are used for regulation of growth of plants as well. Accordingly, when the problem on the safety of agricultural chemicals is further taken into consideration, the present situation is far from the aim of the agriculture of an environment-protecting type.
The agents which are used for the regulation of growth of plants at present are plant growth regulators and their efficacies in promotion of rooting, making the seedlings healthy, prevention of injury at planting, promotion of generation of lateral buds, suppression of axillary buds, promotion of flowering, bearing, thickening, coloration and ripening time, retardation of growth (dwarfing), prevention of fruit drop, prevention of fruit thinning and russet fruit, prevention of phytotoxicity, promotion of adhesion, etc. However, most of the agents are agricultural chemicals mainly comprising synthetic compounds.
Among them, the plant growth regulators used for the retardation of growth (dwarfing) are ancymidol preparations, dikegulac preparations, daminozide preparations, mefluidide preparations, chlormequat liquid preparations, paclobutrazol granules, inabenfide granules, etc. However, all of them contain synthetic compounds as the main ingredients and their use is limited to flowers and ornamental plants, garden plants, fruits and nuts, turf, wheat and rice plant only. Since efficacy of many of the components are dependent upon the concentration upon use, knowledge and experience are required for avoiding the phytotoxicity and choosing the stage of use.
On the other hand, due to a decrease or advancing ages in people for agricultural works or due to a governmental policy of reduction of cultivating field for rice plant in recent years, plan of making the agricultural works efficient and conversion to cultivation of highly value-added field farm products are now being forwarded and, with respect to the object of use of plant growth regulators, utilization meeting with such a change in circumstance is now going on. Thus, in cultivation of leaf and stem vegetables and fruit vegetables which are in an increasing demand, division of labor and utilization of machines in agricultural works are now in progress using cell raised seedling whereby farmers do not prepare seedlings by themselves but purchase the seedlings from other manufacturers who are specialized in raising the seedlings and then said seedlings are cultivated by the farmers for harvest. Under such a system, farmers have no burden for raising the seedling but can devote themselves to just cultivation. Moreover, in leaf and stem vegetables, mechanical planting technique has been developed already for cell raised seedling and, therefore, plan of making the agricultural work efficient and conversion to highly value-added cultivation have been smoothly going on.
However, the biggest disadvantage of this cell raised seedling is that raised seedling grows spindlingly. Especially in a high temperature period such as in summer, spindly growth is significantly accelerated and, when preparation of the field for cultivation is delayed even for a short while, the resulting seedlings are sometimes unable to be used. In addition, plantation by machines is difficult for spindlingly grown seedlings and there is a problem in rooting of the seedling upon transplantation to the final field. Accordingly, there has been a brisk demand for development of dwarfing agents during the seedling stage which are effective for such plants.
As such, there has been a demand for developing an effective dwarfing agent which is a plant growth regulator avoiding the problem of safety in agricultural chemicals and the like, meeting with the trend of agriculture to an environment-protecting type and suppressing the spindly growth of raised seedling in cell raised seedling effective in making the agricultural works efficient and in conversion to highly value-added cultivation. However, at present, such a technique has not been developed yet.
In the meanwhile, the present inventors established a growing technique of disease tolerance seedling by the utilization of two specific strains mutualistically colonizing in the roots of crop plants and already filed a patent application entitled "Plug Mixture for Raising Seedlings and Method for Producing It, and Method for Raising Disease Tolerance Seedlings" (Japanese Patent Application Number Hei-08/149,988). During the course of investigations of a growing technique of such disease tolerance seedlings, the present inventors have found that both of those two specific strains exhibit an excellent dwarfing effect during the growing stage of the seedling of plants and achieved the present invention based upon such a finding.